As a result of development of multi-media, it has become more important to secure an increased visible area (a property of decreasing surface-reflected area when viewing at an angle, which is also called “visibility”) of a display of various displaying devices. A large size displaying device is also required to have well visible display, which is a problem to be solved from technical point of view.
In order to enhance visibility of the displaying device, an antireflection film made of a material having a low refractive index has been formed on a substrate of the displaying device. For forming an antireflection film, there is known, for example, a method of forming a thin film of a fluorine-containing compound by a deposition method. However in the deposition method, it is difficult to form a coating film on a substrate for a large display and yet a cost is high since a vacuum equipment is required.
Such being the case, there have been studied methods of forming an antireflection film by preparing a liquid composition by dissolving a fluorine-containing polymer having a low refractive index in an organic solvent and then coating the obtained composition on a surface of a substrate (for example, JP6-115023A, etc.).
However in the method of coating the fluorine-containing polymer solution, hardness of a coating film is insufficient and therefore the coating film is damaged and peeled off due to abrasion, thereby lowering appearance of a display.
Therefore there have been studied methods of preparing a composition by mixing a photo-curable acrylic monomer, for example, a fluorine-containing acrylic monomer or a fluorine-containing polyfunctional acrylic compound to a fluorine-containing polymer having a low refractive index and after coating the composition, photo-curing the acrylic monomer (JP7-126552A, JP7-188588A, JP8-48935A, etc.).
However in those methods, hardness of the coating film is still insufficient because the fluorine-containing polymer itself which is the main component is not crosslinked. In order to increase the hardness, an amount of the acrylic monomer or the polyfunctional acrylic compound may be increased, but in that case, a refractive index of the cured film is increased and an intended reflection reducing effect is lowered. Also in those methods, the un-reacted acrylic monomer or polyfunctional acrylic compound is apt to remain in the coating film, which causes lowering of physical properties of the cured coating film.
Also methods of mixing a fluorine-containing polymer having a photo-reactive (photo-polymerizable) functional group introduced in its side chain with an acrylic monomer or polyfunctional acrylic compound and photo-curing after coating the mixture have been studied (JP 2527186 and JP 2543903). However the fluorine-containing polymers described therein are high in a refractive index and therefore are insufficient in performance for an antireflection film. In addition, as the number of cure sites of the fluorine-containing polymer is increased to increase hardness, a refractive index becomes high and therefore a reflection reducing effect is further lowered.
An object of the present invention is to provide a curable fluorine-containing polymer which can make its hardness high by photo-curing while maintaining a low refractive index.
Another object of the present invention is to provide an antireflection film possessing improved scratch resistance and abrasion resistance while maintaining a reflection reducing effect and also to provide an antireflection-treated article having such an antireflection film thereon.